Blank adapters and sound suppressors are examples of devices that are sometimes attached to the muzzle of a military style firearm. The muzzle typically includes a flash hider threaded to the end of the barrel and these devices are fitted to the flash hider.
Blank adaptors are used in training to allow the firearm to fire “blank”, as opposed to “live”, rounds of ammunition. If the combustion gases from the firing of a blank are allowed to escape from the unrestricted muzzle of a gun, there is insufficient back pressure to chamber the next round. A blank adaptor restricts the exit of the muzzle so that there is sufficient back pressure for chambering that next round.
A sound suppressor may also be fitted to the end of a gun to absorb the sound and minimize the flash of the fired round so as to reduce the likelihood that the marksman's position will be detected.